Reduced YAP1 expression is involved in megakaryopoiesis during ITP development. (A-B) Flow cytometry analysis of the percentage of YAP1⁺CD41⁺ MKs among CD41⁺ MKs (A) and YAP1⁺CD41⁺CD42⁺ MKs among CD41⁺CD42⁺ MKs (B) (n = 5). (C) Verification of YAP1 and CD41/CD42/CD61 mRNA levels in MKs from the BM of 9 patients with ITP relative to MKs from the BM of 7 healthy controls (HCs) by real-time quantitative polymerase chain reaction (qPCR). (D) Confocal images of immature and mature MKs from patients with ITP and healthy controls after immunostaining for YAP1 (green, YAP1) and MKs (red, CD41). Scale bar, 10 μm. (E) mRNA levels of YAP1 in WT mice before and after ITP establishment (n ≥ 5). (F) Changes in peripheral platelet levels in mice ar antibody administration. (G) Confocal images of BM sections from WT and YAP1^+/− mice after immunostaining for YAP1 (green, YAP1), vascular sinusoids (yellow, laminin A), and MKs (red, CD41). Scale bar, 50 μm. Analysis of MK numbers (left) and number of MKs located around the sinusoids (right; n ≥ 10). (H) Cell clusters in the BM were identified, shown in a t-distributed stochastic neighbor embedding (tSNE) plot. The colors indicate the cell types. (I) Representative gene set enrichment analysis of early and late MKs. (J) Representative Gene Ontology (GO) terms showing differentially expressed genes in the late MK cluster between WT and YAP1^+/− mice. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001. DAPI, 4ʹ,6-diamidino-2-phenylindole; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HC-imMK, healthy control–immature MK; HC-mMK, healthy control–mature MK; ITP-imMK, ITP-immature MK; ITP-mMK, ITP-mature MK; MEP, MK-erythroid progenitor; NES, normalized enrichment score; NK, natural killer cell; PDC, plasma dendritic cell.